I am in alpha16. I have drug policy set to allow it, and they wont take the drugs they are addicted to. It just leads to a lot of mental breaks. I have plenty of the drugs in stockpiles. I am using the mods:
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It is going to be difficult to diagnose the problem from the information provided, as there could be several things causing the problem. First thing to establish is are you having the same problem with the vanilla game or not? If you haven't tested this yet then please do so that it can be ruled out (use the dev mode/God mode to quick build things).
And please post you log file as an attachment.